Based on soft and cracked coal body in thick coal roof of fully enlarged section, cable pulling and serious roof fall accident were easily occurred caused by large loosening deformation pressure in expansion separation of complex geological area. According to caving instability problems during excavation of haulage way roof in 8203 fully mechanized top coal caving face, features of roof deformation were analyzed. At the same time, the main reasons to fall and instability of roof rock were thought as soft coal body and low elongation of anchor cable. In engineering practice, integrity and resistance strength of roof support structures were ensured by adjusting parameters of anchor support, which had a good effect.